The present invention relates to improvements in apparatus for supporting drums for rotation. More particularly, it relates to a multi-element gudgeon assembly that, compared to the one-piece gudgeons of the prior art, is substantially less costly to manufacture, generally more accurate in the support it provides and more durable.
The commonly assigned U.S. patent application Ser. No. 10/054,453 filed on Jan. 22, 2002 entitled xe2x80x9cDRUM-LOADING/UNLOADING APPARATUS FOR ELECTROSTATOGRAPHIC PRINTER/COPIERxe2x80x9d, discloses an image-recording drum assembly that is adapted for use in an electro-statographic printer/copier to record latent electrostatic images. Referring to the cross-sectional illustration of FIG. 1, such drum assembly includes a hollow cylindrical drum 10 (i.e., a rigid tube or sleeve) supported at opposite ends by front and rear gudgeons 12, 14, respectively. Drum 10 is made of aluminum, and it is provided with an outer layer 11 of photoconductive material on which electro-static images can be formed and developed by the well-known electro statographic imaging process. Each of the drum""s supporting gudgeons 12, 14 is basically a unitary (i.e., one piece) structure, preferably being made, for example, of aluminum to facilitate its manufacture. Further, each gudgeon is machined from a metal form so as to define a central collar or sleeve portion (12A, 14A), and an integral, radially-extending circular flange portion (12B, 14B). Each sleeve portion has an axial circular bore with a diameter that is adapted to receive and grasp (via an interference fit) a desired cylindrical portion of a rotatably-driven drive shaft or axle 16. In use, axle 16 serves to rotate the gudgeons, and the drum they support, about the axle""s longitudinal axis A.
The rear portion of the drive shaft 16 carries a pair of bearings B1, B2 by which the rear portion of the drum assembly can be supported for rotation. Each of the gudgeon""s radially-extending circular flange portions (12B, 14B) terminates to define a tapered circular rim R that is shaped to engage, center and support the respective tapered ends of drum 10 as the gudgeons are caused to move axially towards each other, as explained below.
In contrast with the rear gudgeon 14 of the above-described drum assembly, the front gudgeon 12 further defines a stub-axle portion 12C that carries a bearing B3 by which the front of the drum assembly is also supported for rotation. Further, to enable removal of the drum portion of the drum assembly, e.g., for servicing or replacement, the front gudgeon 12 is provided with a releasable, radially-expandable coupling 20 by which the gudgeon can be readily disconnected and removed from the axle 16. Upon disconnecting the front gudgeon from the axle, drum 10 can slide axially, away from the rear gudgeon 14 and off the forward end of the axle. Coupling 20 is housed within the sleeve portion 12A of gudgeon 12, forward of that portion of the axle engaged by the sleeve. Activation of the coupling 20 is effected by a threaded rod 18 that passes axially through a bore hole formed in the stub axle portion 12C of the gudgeon. Rod 18 has an integral platform 18A of enlarged diameter and a threaded end 18B that is adapted to be received by a threaded bore hole 16A formed in the forward end of axle 16. As rod 18 rotates in a direction to engage the threaded end of rod 18 with the borehole 16A, the front gudgeon is drawn towards the rear gudgeon, and the drum 10 becomes seated on the respective gudgeon rims R. Continued rotation of rod 18 causes the radially expandable coupling 20 to be compressed against a stiff coil spring 22. Axial movement of the coil spring is limited by a retainer ring 23 projecting from a circular groove 12D formed in the inner wall of sleeve portion 12A. As the coupling 20 compresses axially, it expands radially, thereby engaging the inner wall of the gudgeon""s sleeve portion 12A tightly securing the gudgeon 12 to the axle 16. The unitary front gudgeon of the prior art is better shown in the cross-sectional illustration of FIG. 2.
From the foregoing description and illustration in FIG. 2, it will be appreciated that the unitary front gudgeon 12 is a relatively complex structure that requires precision machining to achieve a desired minimal runout of the overall drum assembly. In machining the front gudgeon from a single block of aluminum, it may be appreciated that it is difficult to cut the inside bore of the sleeve portion 12A to the depth required to house the axle and coupling assembly while maintaining a close tolerance on this central bore hole. It will be appreciated that, owing to the shape of the stub axle 12C, the central bore of sleeve portion 12A can be accessed from only one end. Thus, the deeper the bore in the sleeve portion, the more difficult it is to maintain the requisite control of the cutting tool, and variations from a nominal circular cross-section begin to occur. Further, the use of aluminum for the entire gudgeon represents a compromise between materials that are relatively easy to machine, and those that provide an extended wear capability. Ideally, at least the sleeve portion 12A that houses the movable components of the coupling 20 should be made of a harder and more durable metal than aluminum. But to manufacture the gudgeon entirely from steel, or the like, would add significantly to manufacturing costs.
In view of the foregoing, an object of this invention is to provide a gudgeon assembly which overcomes the above-noted manufacturing, accuracy and durability problems associated with the one-piece gudgeon structures of the prior art.
In accordance with the invention, an improved gudgeon of the type described above with reference to the xe2x80x9cfrontxe2x80x9d drum-supporting gudgeon is provided. According to a preferred embodiment of the invention, such gudgeon takes the form of a multi-element assembly including a cylindrical sleeve element, a flange element, and a stub axle element. The cylindrical sleeve element defines a cylindrical central bore of substantially uniform diameter, such bore being adapted to receive one end of an axle. The flange element includes an inner collar portion slidably mounted on the outer surface of the cylindrical sleeve element, and has an outer rim portion adapted to engage, center and support the end of a cylindrical drum. The stub axle element is mounted on one end of the cylindrical sleeve element and cooperates with structure on the sleeve element to position the flange element at a fixed desired location on the sleeve element. Preferably, the stub axle element is provided with a central bore adapted to receive a threaded rod which, in turn, is adapted to engage a threaded opening in the free end of an axle positioned within the sleeve""s central bore in order to adjust the axial position of the gudgeon assembly relative to the axle. Preferably, the sleeve and stub axle elements are made of hardened steel, whereas the flange element is made of aluminum with a hard coat to prevent wear.
By fabricating the gudgeon of the invention from three independent elements, each being readily manufactured to precise standards, the overall precision and reproducibility of the gudgeon assembly are enhanced. Further, being able to select different materials for each component has the effect of improving the reliability and durability of the assembly.
The invention, and its objects and advantages, will become more apparent in the detailed description of the preferred embodiment presented below.